The purpose of this study is to determine if a calcium channel blocker (Amlodipine) can prevent or ameliorate cyclosporin or tacrolimus-induced nephrotoxicity in children after orthtopic liver transplantation (OLT) as measured by glomerular filtration rate (GFR) and renal function tests. Subjects are now being enrolled in the "prospective" arm of the study which involves serial GFR measurement before and up to one year after OLT. During this study period 7 subjects have been enrolled and 2 have been transplanted but not completed all follow-up studies.